As a result of recent efforts to develop practical means for removing particulates from diesel engine exhaust gases in automotive vehicles, it has been found that wall-flow ceramic monolith filters can provide very efficient filtration of diesel exhaust particulates with relatively low pressure drop. U.S. Patent application Ser. No. 99,933 filed Dec. 3, 1979 in the names of Morris Berg, William Johnston and Carl Schaffer and assigned to the assignee of the present invention, discloses examples of such ceramic monolith filters.
While such filters have been shown to be highly effective in the collection of diesel exhaust particulates, it appears that the volume of particulates collectable from diesel engine exhaust products requires that exhaust filters be replaced or regenerated at frequent intervals if the size of the filter elements is limited to volumes presently considered practical. Thus, to avoid the need for frequent servicing of such a system it appears desirable to provide means for periodic regeneration of the filter element by incineration of the collected exhaust particulates at intervals during normal operation of the vehicle.
To accomplish this, it has been proposed that exhaust gases passing into the filter be periodically heated to the particulate ignition temperature. A suggested manner of such heating is the method of engine throttling proposed in U.S. Patent application Ser. No. 952,710, filed October 19, 1978, in the names of Otto Ludecke and Theodore Rosebrock, and assigned to the assignee of the present invention. However, tests have indicated that incineration of particulates in porous wall-flow ceramic monolith filters by inlet gas heating would be difficult to initiate and to complete. In addition, other proposed methods of heating would apparently require a very large expenditure of outside energy.